1. Field of the Invention
The present invention is generally related to an engine valve system and, more particularly, to a valve lash adjustment nut that is configured to reduce the likelihood of wear that would otherwise degrade the positional accuracy of the valve actuation apparatus.
2. Description of the Related Art
Those skilled in the art of internal combustion engines are familiar with many different techniques and devices that can be used to control or adjust valve lash. Some valve trains for internal combustion engines utilize a mechanical lash adjustor which consists of a threaded ball stud and a jam nut to inhibit rotation of the ball stud and the resulting degradation of positional accuracy that can be caused by inadvertent rotation of the ball stud. In some applications, the ball stud and jam nut are made from high strength steel and the portion of the internal combustion engine head with which they interface is typically provided with an insert made of steel or another hard material. Variations of valve trains and lash adjustment mechanisms have been developed and improved over many years.
U.S. Pat. No. 3,096,750 which issued to Bouvy et al. on Jul. 9, 1963, describes an overhead camshaft engine valve mechanism. It has a simplified valve train construction in which rocker shafts are eliminated and simple inexpensive valve train elements are employed between conventional camshaft lobes and each engine valve stem.
U.S. Pat. No. 3,532,080, which issued to Saruta et al. on Oct. 6, 1970, describes a device for driving poppet valves of an engine. A low noise device for driving poppet valves of an overhead cam engine is described. The valves are actuated by rocker arms selectively rotated by cams. A bias spring is provided for each rocker arm so as to keep the rocker arm always in contact with the cam.
U.S. Pat. No. 3,791,355, which issued to Bergmann et al. on Feb. 12, 1974, describes a mechanical lash adjustor for overhead cam engines. The mechanism is intended for use as a direct replacement for a hydraulic lash adjustor in overhead cam engines. It includes a stud threaded into an insert and having means at one end for supporting a rocker arm. The insert is designed to fit directly into an opening provided in a conventional engine head.
U.S. Pat. No. 4,519,345, which issued to Walter on May 28, 1985, describes an adjustable ratio rocker arm. Adjustments to the amount of valve lift in an engine are readily made by corresponding adjustments to the location at which a cam actuated push rod contacts the push rod side of the valve actuating rocker arm. The device provides an accurate and rapid means for adjusting the push rod contact position by slotting the push rod side of the rocker arm and fitting a square adjustment plate against a fixed index on top and bottom surfaces of the push rod side.
U.S. Pat. No. 4,638,772, which issued to Burandt on Jan. 27, 1987, describes a valve actuating apparatus for minimizing the need for lash adjustment. A cam unit and a follower are configured so that the surfaces between which lash is measured are for all intent and purposes removed or segregated from the surfaces used for effecting valve movement. The modified interaction between the cam and the surface the cam bears against compensates for reduction in valve lash.
U.S. Pat. No. 5,645,025, which issued to Caya et al. on Jul. 8, 1997, describes an internal combustion engine which includes a cast cylinder head having as-cast alignment ribs that align a squared-off fulcrum in the rocker assembly. The rocker arm also has two substantially flat surfaces that engage the planar sides of the fulcrum to minimize lateral movement of the rocker arm.
U.S. Pat. No. 7,383,799, which issued to Wynveen et al. on Jun. 10, 2008, discloses a method for monitoring the operating condition of an engine valve system. A system is provided for monitoring changes in the operation of a valve system of an engine. An accelerometer provides vibration related signals that are obtained by a microprocessor or similarly configured device and compared to a reference or baseline magnitude. The obtaining step can comprise the steps of measuring, filtering, rectifying, and integrating individual data points obtained during specific windows of time determined as a function of the rotational position of the crankshaft of the engine. These windows in time are preferably selected as a function of the position of exhaust or intake valves as they move in response to rotation of cams of the valve system.
U.S. Pat. No. 7,363,893, which issued to Rohe et al. on Apr. 29, 2008, describes a system for variable valvetrain actuation. An electromechanical variable valvetrain actuation system for controlling the poppet valves in the cylinder head of an internal combustion engine is described. The system varies valve lift, duration, and phasing in a dependent manner for one or more banks of engine valves. A rocker subassembly for each valve or valve pair is pivotally disposed on a control shaft between the cam shaft and the roller finger follower. The control shaft may be displaced about a pivot axis outside the control shaft to change the angular relationship of the rocker subassembly to the cam shaft, thus changing the valve opening, closing, and lift.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
In engines with aluminum cylinder heads that do not use a steel insert, there can be insufficient strength in the aluminum threads for proper retention at the jam nut to head interface. As a result, during each valve event, the jam nut to head interface can slip from side to side. As a result, the contact surfaces of the jam nut and head can become worn as a result of abrasion. This wear can loosen the contact between the jam nut and the engine head, resulting in a change in valve lash. If the contact surfaces of the jam nut and engine head are perpendicular to the central axis of rotation of the jam nut, the arrangement is particularly sensitive to wear of either or both of these contacting surfaces as a result of relative movement between them that can result from vibration caused by repetitive valve events. It would therefore be significantly beneficial if the wear of the jam nuts could be decreased or completely inhibited.